The present embodiments relate to phase change ink compositions characterized by being solid at room temperature and molten at an elevated temperature at which the molten ink is applied to a substrate. These phase change ink compositions can be used for ink jet printing, and provide robust image quality on various substrates, including coated substrates, which are generally difficult to print on. The present embodiments provide the phase change ink composition with photochromic additives which provide a robust ink for use in security applications. The present phase change inks comprise an amorphous component, a crystalline material, one or more photochromic additives, and optionally a colorant, and methods of making the same.
Ink jet printing processes may employ inks that are solid at room temperature and liquid at elevated temperatures. Such inks may be referred to as phase change inks, hot melt inks, phase change inks and the like. For example, U.S. Pat. No. 4,490,731, the disclosure of which is totally incorporated herein by reference, discloses an apparatus for dispensing phase change ink for printing on a recording medium such as paper. In thermal ink jet printing processes employing hot melt inks, the phase change ink is melted by the heater in the printing apparatus and utilized (jetted) as a liquid in a manner similar to that of conventional thermal ink jet printing. Upon contact with the printing recording medium, the molten ink solidifies rapidly, enabling the colorant to substantially remain on the surface of the recording medium instead of being carried into the recording medium (for example, paper) by capillary action, thereby enabling higher print density than is generally obtained with liquid inks. Advantages of a phase change ink in ink jet printing are thus elimination of potential spillage of the ink during handling, a wide range of print density and quality, minimal paper cockle or distortion, and enablement of indefinite periods of nonprinting without the danger of nozzle clogging, even without capping the nozzles.
In general, phase change inks (sometimes referred to as “solid inks” or “hot melt inks”) are in the solid phase at ambient temperature, but exist in the liquid phase at the elevated operating temperature of an ink jet printing device. At the jetting temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the recording medium, either directly or via an intermediate heated transfer belt or drum, they quickly solidify to form a predetermined pattern of solidified ink drops.
Phase change inks for color printing typically comprise a phase change ink carrier composition which is combined with a phase change ink compatible colorant. In a specific embodiment, a series of colored phase change inks can be formed by combining ink carrier compositions with compatible subtractive primary colorants. The subtractive primary colored phase change inks can comprise four component dyes or pigments, namely, cyan, magenta, yellow and black, although the inks are not limited to these four colors. These subtractive primary colored inks can be formed by using a single dye or pigment or a mixture of dyes or pigments. For example, magenta can be obtained by using a mixture of Solvent Red Dyes or a composite black can be obtained by mixing several dyes. U.S. Pat. No. 4,889,560, 4,889,761, and 5,372,852, the disclosures of each of which are totally incorporated herein by reference, teach that the subtractive primary colorants employed can comprise dyes from the classes of Color Index (C.I.) Solvent Dyes, Disperse Dyes, modified Acid and Direct Dyes, and Basic Dyes. The colorants can also include pigments, as disclosed in, for example, U.S. Pat. No. 5,221,335, the disclosure of which is totally incorporated herein by reference. U.S. Pat. No. 5,621,022, the disclosure of which is totally incorporated herein by reference, discloses the use of a specific class of polymeric dyes in phase change ink compositions.
Phase change inks are desirable for ink jet printers because they remain in a solid phase at room temperature during shipping, long term storage, and the like. In addition, the problems associated with nozzle clogging as a result of ink evaporation with liquid ink jet inks are largely eliminated, thereby improving the reliability of the ink jet printing. Further, in phase change ink jet printers wherein the ink droplets are applied directly onto the final recording medium (for example, paper, transparency material, and the like), the droplets solidify immediately upon contact with the recording medium, so that migration of ink along the printing medium is prevented and dot quality is improved.
While the above conventional phase change ink technology is successful in producing vivid images and providing economy of jet use and substrate latitude on porous papers, a need remains for additional means for robust printing for security applications on various substrates, including coated paper substrates. As such, there is a need to provide novel compositions for phase change ink compositions and security printing technologies to provide customers with excellent image quality on all substrates.
Each of the foregoing U.S. patents and Patent Publications are incorporated by reference herein. Further, the appropriate components and process aspects of the each of the foregoing U.S. patents and Patent Publications may be selected for the present disclosure in embodiments thereof.